1. Field of the Invention
This invention relates to an improved process for producing salt free N-acyl taurides, i.e. N-acyl taurine salts. More particularly, this invention relates to an improved process for preparing carboxylic acid amides of 2-aminoalkane sulfonic acids. Additionally, this invention relates to a novel process for purifying such taurides from a reactant mixture.
2. Prior Art
N-higher acyl taurides are well known wetting, cleansing, softening, dispersing and surface active agents and generally have the formula: ##STR1## in which ##STR2## is a higher acyl radical having about 6 to about 22, carbon atoms, X is hydrogen or an alkyl radical having from 1 to 20, preferably 1-4 carbon atoms and M is an alkali metal, alkaline earth metal, magnesium, ammonium or substituted ammonium substituent. The process of reacting higher fatty acids, fatty acid chlorides and fatty acid esters with 2-aminoalkane sulfonic acids (taurines) and their alkaline metal salts to produce such agents is also well known.
One of the first patents in this area was U.S. Pat. No. 1,932,180 to Guenther, et al. (issued 1933). Several processes are described therein for the preparation of such materials. Guenther, et al. describes three types of processes:
(1) A free fatty acid dissolved in an aliphatic amine is mixed with an amino-alkane sulfonic acid (taurine) and then heated to boiling; PA1 (2) An alkyl ester of a fatty acid is heated with the sodium salt of an amino alkane sulfonic acid; and PA1 (3) A carboxylic acid chloride is treated in aqueous medium with 2-amino-alkane sulfonic acid in the presence of caustic soda. PA1 R is a C.sub.8 -C.sub.22 hydrocarbon radical; R.sub.1 is H or C.sub.1 -C.sub.20 hydrocarbon radical; and PA1 R.sub.2 and R.sub.3 are each independently, H or a C.sub.1 -C.sub.6 hydrocarbon radical; and PA1 M is alkali metal, e.g. Li, K, or preferably Na. PA1 U.S. Pat. No. 2,974,153 to Gajewski; PA1 U.S. Pat. No. 2,974,154 to Schenck; PA1 U.S. Pat. No. 2,987,526 to Schenck; PA1 U.S. Pat. No. 3,013,035 to Huber, et al.; PA1 U.S. Pat. No. 4,233,229 to Chakrabart; and PA1 U.S. Pat. No. 4,352,759 to Schwartz. PA1 U.S. Pat. No. 2,880,219 to Burnette; PA1 U.S. Pat. No. 2,967,872 to Lorentzen; PA1 U.S. Pat. No. 3,150,156 to Lamberti; and PA1 U.S. Pat. No. 3,232,968 to Schenck. PA1 R.sub.1 is H or a C.sub.1-20 hydrocarbon radical: PA1 R.sub.2 and R.sub.3 are each, independently H, or a C.sub.1 -C.sub.6 hydrocarbon radical; and PA1 M is an alkali metal or alkaline earth metal. PA1 a. Amidation reaction times are unexpectedly reduced, for example, from 10 hrs. to 2 hrs. This is an advantage, not only in reduction of reaction time but in the reduction of the degradation of the tauride produced and maintaining the integrity of color. PA1 b. High conversions with negligible amounts of other fatty matters such as fatty acid anhydrides, fatty soaps which are likely by-products of high temp. reactions. By titrations for activity, Free Fatty Acids and N-methyltaurine (NMT) by alkalinity, up to and greater than 99% of a the mass can be accounted for in the Taurates of this invention. In our experiments, use of SBH is candidly showing an advantage of reducing the other fatty matter to nearly negligible amounts. Prior art (Burnette, U.S. Pat. No. 2,880,219) has expressly mentioned the presence of other fatty matter to be analyzed by either extractions. Our invention produces the product that gives&gt;99% of material balance as activity+FFA+NMT in the crude Acyl-Taurate of Amidation Rxn. and such analysis is simply and promptly done without resorting to ether-extractions.
This latter process, the most commonly used commercial process is described by Kastens and Mayo., in Ind. & Eng. Chem., vol. 42, pp. 1626-1638, 1950 and is referred to as the "Schotten-Baumann reaction".
In this process when the acid chloride is treated with a taurine or a taurine salt, a reaction mixture containing the N-acyl taurine is obtained which contains a considerable quantity of salt, i.e. sodium chloride. This salt is highly undesirable. Also, during the process appreciable hydrolysis of the acyl chloride occurs, resulting in the formation of soap as a byproduct.
This "Schotten-Baumann reaction" may be illustrated by the following equation: EQU RCOCl+HNR.sub.1 --CHR.sub.2 --CHR.sub.3 --SO.sub.3 M+MOH.fwdarw.RCONR.sub.1 --CHR.sub.2 --CH--R.sub.3 --SO.sub.3 M+MCl+H.sub.2 O II
wherein
The N-acyl taurines and their salts produced by the aforementioned process are sold under the trademark IGEPON by GAF, Incorporated (now Rhone-Poulenc).
There are many disadvantages to the production of such compounds by this "acid chloride" route. In particular, The preparation of the acid chloride employed as an intermediate in the above process is not only hazardous, but time consuming and costly to make, since it employs phosphorous trichloride and adds an additional step to the process. Further, an alkaline agent is required to neutralize the hydrogen chloride formed by the acyl chloride.
Still further, there is usually a side reaction according to the following equation: EQU RCOCl+2MOH.fwdarw.RCOOM+MCl+H.sub.2 O III
Thus, the formation of inorganic chloride salts and usually soap is unavoidable in this acid chloride route of making acyl taurides.
Another disadvantage is that the aforedescribed reaction (II) does not readily go to completion without the use of excess taurine salt. Thus, unreacted taurine salt, is usually present in the final reaction product.
Still further, the aforementioned chloride, soap and amine impurities are difficult to separate from the acyl tauride if a pure product is desired. More importantly, the presence of a chloride salt such as sodium chloride with the acyl tauride is undesirable because the salt imparts hygroscopicity and corrosiveness to the product.
Various improvements and modifications of the acyl chloride method for making acyl taurides have been proposed in order to reduce the formation of these undesirable byproducts. The suggested modifications have not successfully eliminated undesirable byproduct formation and have generally involved carefully controlled operating conditions and complex purification systems.
A proposed process for making acyl tauride which eliminates some of the aforedescribed processes involves a reaction of a free fatty acid with a taurine salt, for example, according to the following equation: ##STR3##
In order for this reaction to take place, however, the removal of water and the use of high temperatures and an inert atmosphere are necessary. It was also found that considerable taurine decomposition occurred, i.e. the separation of ammonia or methyl amine from the taurine, resulting in poor product yields and quality, e.g. odoriferous and discolored.
There have been many prior art attempts to solve the aforedescribed problems for producing substantially pure N-acyl taurines and their salts. One type method of solving these problems is to use the acid chloride based process, which produces salt and other contaminants, and then attempt to purify the resultant reaction products, see for example, the following U.S. patents:
Another type method of solving the aforedescribed problems is to avoid the production of such contaminants by using the direct amidation process or improvements thereon, see, for example, the following U.S. patents:
None of these processes have been particularly successful, i.e. the acid chloride process requires cumbersome and costly purification to produce the desired product and the direct amidation process does not result in the required high quality products and thus also requires a cumbersome and costly purification to remove the unreacted starting materials.
More specifically:
U.S. Pat. No. 2,880,219 to Burnette (issued 1959), describes a direct amidation process which comprises acylating a taurine salt in an inert atmosphere at a temperature of about 200.degree. to 320.degree. C. while removing the water formed during the reaction. Applicant has noticed when using this process, undesirable dark tan products are produced.
U.S. Pat. No. 2,967,872 to Lorentzen (issued 1961), describes another direct amidation process comprising reacting a high molecular weight fatty acid anhydride with one mole of a taurine salt in aqueous solution. The reaction product is a mixture of taurides and free-higher molecular weight fatty acids substantially free from inorganic salts, soaps and unreacted taurine salt. The N-methyl-N-acyl-taurate is purified from the reaction mixture by extraction with acetone, or an aqueous ethanol solution or by precipitation of the free fatty acids after conversion into the calcium soaps.
U.S. Pat. No. 2,974,153 to Gajewski (issued 1961), describes an acid chloride based process for preparing N-acyl taurine. The process consists of mixing in an aqueous slurry an N-higher acyl taurine, an alkaline metal chloride or sulfate and an aliphatic or alicyclic mono carboxylic acid or its ester. The mixture produced settles into a lower aqueous phase and an upper oil phase. The oil phase is then separated from the aqueous phase at a temperature above the solidification point of the solvent system. The process, in essence is the liquid extraction of the salt from the reaction mixture of the tauride and free fatty acid. The final purified product comprises the tauride, unreacted free fatty acids and negligible amounts of salt and moisture.
U.S. Pat. No. 2,974,154 to Schenck (issued 1961), is similar to the aforedescribed Gajewski acid chloride based process. Schenck describes adding to an aqueous slurry of the N-higher acyl taurine and water soluble salt an aliphatic or alicyclic monocarboxylic acid or its ester to form a solvent system, heating the system to distill off the water, and then separating the crystallized salt, e.g. alkali metal chlorides and sulfates from the mixture at a temperature above the solidification point of the taurine or aliphatic or alicyclic monocarboxylic acid. This process, in essence, is the distillation of the water from the reaction mixture until it is nearly anhydrous and then subjecting the anhydrous mixture to hot filtration. The product yield comprises the moisture free tauride, which is free of fatty acids and has a negligible amount of sodium chloride therein.
U.S. Pat. No. 2,987,526 to Schenck (1961), describes an acid chloride based process consisting of reacting an alkali metal salt of the taurine or taurine derivative in an aqueous slurry or solution with a fatty acid chloride under specific conditions of temperature and in the presence of a particular organic solvent and alkali metal hydroxide to produce an N-acyl taurine which is salt free and free from traces of other water soluble impurities including unreacted taurine or taurine derivatives. The solvent may be acetone, dioxane or methyl ethyl ketone.
U.S. Pat. No. 3,013,035 to Huber, et al. (issued 1961), describes another acid chloride based process wherein a sufficient amount of sodium or potassium hydroxide is added either simultaneously or intermittently to maintain the pH level of the reaction mixture above 7.
U.S. Pat. No. 3,150,156 to Lamberti (issued 1964), describes a direct amidation process comprising reacting a fatty acid with a taurine salt in the presence of a catalyst of water soluble alkali metal phosphites and hypophosphites. The reaction temperature used is 220.degree. C. which is above the decomposition temperature of the catalysts used. The decomposition products can be toxic and explosive.
U.S. Pat. No. 3,232,968 to Schenck (issued 1966), describes a direct amidation process comprising admixing an acylating agent, e.g. aliphatic monocarboxylic acids with a catalytic amount of hypophosphorous acid, adding a taurine salt and then heating the resulting mixture to a temperature of 140.degree.-320.degree. C. while removing the water formed during the reaction. This catalyst is subject to decomposition below the reaction temperature used to toxic and explosive products.
U.S. Pat. No. 3,234,247 to Abend, et al. (issued 1966), describes reacting a fatty amide with sodium isethionate in the presence of a basic catalyst to produce N-acyl taurates. The reaction is carried out in the presence of hazardous solvents, e.g. glycol ethers, which can be difficult to remove in order to obtain the high purity products desired.
U.S. Pat. No. 4,233,229 to Chakrabarti, describes an acid chloride based process for preparing substantially salt free N-acyl taurine by reacting a carboxylic acid chloride with a taurine salt in an aqueous lower alkanol solution and an alkaline metal hydroxide followed by separating the insoluble precipitated alkaline metal chloride from the alkanolic reaction mixture at a temperature high enough to solubilize the N-acyl taurine reaction product followed by the cooling reaction medium low enough to precipitate the desired N-acyl taurine. The purified product contains up to 1.5% sodium chloride and is thus not totally salt free.
U.S. Pat. No. 4,352,759 to Schwartz (issued 1982), describes a method of recovering high purity N-acyl taurine in high yield from reaction products from the acid chloride based process. The recovery involves solubilizing the crude N-acyl tauride reaction product in an aqueous alkanol solvent medium at an elevated temperature, then cooling the solution to a lower temperature where a high purity N-acyl taurine crystallizes in high yield while salt and other impurities remain in solution and thereafter filtering the crystalline material. The press cake is given multiple washes with methanol. The process is time consuming.
Sodium Borohydride is a well known reducing agent, or activator for use in many processes, see for example U.S. Pat. Nos. 5,136,071 to Bank et al., 5,178,665 to Hague, 5,182,046 to Patton, et al., and 5,250,554 to Naka et al., however none of these patents teach or suggest the use of such compound in a process for producing N-acyl taurides or compounds similar thereto.